10 August 2023
Strictly speaking, chemoprevention is the administration of specific drugs to prevent the onset of certain cancers in people at high risk of developing them, as well as to cancer patients to help prevent their cancer from coming back.
That said, this definition has been widening throughout the years to include potential chemopreventive substances that are not necessarily drugs. So-called “nutraceuticals”, such as dietary fiber, prebiotics, probiotics, polyunsaturated fatty acids, antioxidants (such as vitamins) and different types of herbal or natural foods (dietary supplements) are also being studied for cancer chemoprevention. However, to date, the efficacy of these substances has not been confirmed. Be as it may, obesity and diabetes being known to increase the risk of cancer, dietary habits that help prevent these diseases can also potentially help to prevent cancer.
Going back to the stricter definition, there are well-known examples of cancer chemopreventive drugs in the field of breast cancer. Tamoxifen and raloxifene, called SERMs (for selective estrogen receptor modulators), help prevent breast cancer by interfering with estrogen, the female sex hormone involved in cancer development. However, these drugs are not devoid of side effects, so they are mostly given prophylactically to women at very high risk for breast cancer, due in particular to a strong family history of the disease.
There are also two vaccines that are actually cancer-preventing drugs. One is the hepatitis B vaccine: it prevents infection by the hepatitis B virus, which can cause liver cancer. The other is the HPV vaccine, which prevents infection by several strains of the human papillomavirus (HPV), which can lead to cervical cancer. Vaccines preventing other cancers are being actively studied.
Other drugs yet are potentially seen as cancer chemopreventive substances. This is the case of aspirin, for which there is evidence that long-term use may contribute to prevent colon cancer. But here too, studies have given mixed results. Besides, aspirin is also notoriously known for causing serious side effects such as bleeding in the stomach and brain.
Effective cancer chemoprevention has still a long way to go. Numerous clinical trials are ongoing.
Sources:
https://www.cancer.gov/
https://www.oncolink.org/
https://www.guysandstthomas.nhs.uk/
https://www.mayoclinic.org/
